Vehicle emission control systems may be configured to store refueling vapors, running-loss vapors, and diurnal emissions in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to engine intake for combustion, further improving fuel economy for the vehicle. In a typical canister purge operation, a canister purge valve coupled between the engine intake and the fuel vapor canister is opened, allowing for intake manifold vacuum to be applied to the fuel vapor canister. Fresh air may be drawn through the fuel vapor canister via an open canister vent valve. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
However, engine run time in hybrid vehicles and plug-in hybrid vehicles may be limited, and thus opportunities for purging fuel vapor from the canister may also be limited. If the vehicle is refueled, saturating the canister with fuel vapor, and then parked in a hot, sunny location prior to a purge event, the canister may desorb fuel vapors as it warms up, leading to bleed emissions. For vehicles that vent the fuel tank during a vehicle-off condition, the volatilization of fuel under similar conditions may overwhelm the capacity of the fuel vapor canister.
One approach for addressing these problems is described in U.S. Pat. No. 4,732,588 to Covert et al. Therein, a thermo-electric cooler is deposed at a canister inlet and activated when the vehicle engine is turned off. However, the inventors herein have recognized potential issues with such systems. For example, the thermo-electric cooler is powered by the vehicle battery, and no conditions are indicated for selectively activating the thermo-electric cooler, or for de-activating the cooler during a lengthy vehicle-off soak. As such, the vehicle battery may be drained, even if cooling the canister is not necessary based on operating conditions. This may lead to scenarios wherein the battery does not sustain enough charge to power a subsequent engine ignition.
In one example, the issues described above may be addressed by a method for a vehicle. During a first condition, including a vehicle-off condition and a vehicle sun exposure greater than a threshold, one or more cooling elements coupled to a fuel vapor canister are activated, and one or more cooling fans are activated to dissipate heat generated by the one or more cooling elements. In this way, desorption of fuel vapors from the canister to the atmosphere may be decreased when the vehicle is parked in the sun, when bleed emissions are likely to occur in the absence of canister cooling.
As one example, the cooling elements and cooling fans may be powered by solar cells, operative to convert solar radiation incident thereon into electrical energy. In this way, bleed emissions may be reduced without compromising vehicle battery charge. Further, during conditions where bleed emissions are most likely to occur (i.e. hot and sunny days), ample energy to supply the cooling elements and cooling fans may be readily available. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.